Birthday matters

Does it matter which month you’re born in?

Based on the results of the 20 lakh students taking the Class XII exams at Tamil Nadu over the last 3 years (via Reportbee), it appears that the month you were born in can make a difference of as much as 120 marks out of 1,200 – or 10%!

Most students who took the Class XII exams in 2011 were born between March 1991 and June 1992. The average marks of each student (out of 1200) is shown in the graph below.


Students born in June 1991 scored the lowest – around 720/1200. This suddenly shoots up in July, then in August, and the students born in September score as much as 840/1200 on average. From there on, it’s downhill.

This result is consistent across years. In 2009 and 2010, you see a similar pattern.

tn-2009 tn-2010

Why could this be?

Malcolm Gladwell’s book Outliers offers a clue.

Outliers opens, for example, by examining why a hugely disproportionate number of professional hockey and soccer players are born in January, February and March.

The answer turns out to be completely unrelated to numerology or astrology.

It’s simply that in Canada the eligibility cutoff for age-class hockey is January 1. A boy who turns ten on January 2, then, could be playing alongside someone who doesn’t turn ten until the end of the year—and at that age, in preadolescence, a twelve-month gap in age represents an enormous difference in physical maturity.

In Tamil Nadu, students must be 5 years old before entering Class 1. Schools open mid-June. So students born in June 1994 would barely make it in June 1999 – making them the youngest students in the class. July and August students would be missed – but since many schools implement this policy leniently, they sometimes make it in as well. September borns are often consistently the eldest students in a class.

This pattern reflected in the marks. The eldest – the September 1993 borns – score the highest. The next eldest, the October 1993 borns, score a bit less. And so on. (There are older students who take the exam – the ones born before September 1993 – but many of these are failed students from the previous year, introducing a bias in the results.)

Perhaps this initial advantage that the elder students have over their classmates continues through the years? Whatever the reason, it’s clear that if your child is born in September, he or she already has a 100 mark advantage!

  1. abhijeet says:

    “Whatever the reason, it’s clear that if your child is born in September, he or she already has a 100 mark advantage!”

    But at the cost of being older and “losing” 8-9 months!

  2. Shankar V says:


    Thank God I was born in July! If not on the crest, I at least made it into the upward curve! 😉

  3. S Anand says:

    @abhijeet: That reminds me of the “Life is a race” dialogue in 3 Idiots 🙂

    Well, not sure how bad being a bit older is. I personally don’t mind, but maybe others do?

  4. Shailesh says:

    Oh…now I know why I was getting good marks…. 🙂
    I am born in September…and my headmaster changed my birthdate (to Jul month) in school register to not waste my 8-9 months…..

  5. ravi atluri says:

    They made me study LKG “TWICE”, because I was born in September and didn’t have enough time to be 3! and I have been an anomaly to the september-born-high-performers trend.

    If the marks are related to the mugging capacity, which if related to age would explain the graphs only for the schooling during. Would like to see, how would these change in college and bachelors 😀

    One more doubt, I have is, many parents have the dob’s of after-aug-born’s to sometime between may to june. If that’s the case, the months on the graph have to be offset 😉

  6. S Anand says:

    @Shailesh — if you got into school early, then statistically, you had a DISadvantage. So guess you were MUCH brighter than your classmates!

    @Ravi — true. No idea how to correct for the real date of birth, though…

  7. k says:

    this is similar to the paper on Israeli schools where an externally imposed rule created a disproportionate class size, which helps in identifying the effect of class size on performance.

    date of birth can help in identifying the effect on performance then.

  8. Vasant says:

    Ha! Now I know why I scored so less in the boards. It’s when I was born! 🙂

    Jokes aside, brilliant analysis.

  9. Sathya says:

    Good One !
    If you still have access to data, would it be possible to plot the same graph against their “numerology numbers” ? ie., 28th born would be 2+8 = 10 => 1+0 = 1. I used to wonder that astrology ( perhaps numerology ) could provide certain insights and that it astro/numero predictions should be verified using statistics. ( Pls note that I do not suggest astro determines a person’s fate. But perhaps it can predict events with some accuracy. How a person reacts to those events are not in the realm of astrology).
    I would love to do this if I had access to the data. In case you find it worthwhile, it would be interesting to see if numero number matters at all !

  10. Swetha says:

    M a September born and a gold medalist . (*Grins*)

  11. Sumit Dhar says:

    And, I know this is extremely difficult, but was wondering if it would be possible to assess the impact of month in which you were born on your professional growth / salary growth. Or even more simply, if marks are correlated with professional success.

    We Indians tend to believe that good marks == success at work. Would love to know if data validates this belief.

    If only this kind of data were available… Maybe HR teams in organizations could perform such an assessment.


  12. Vish says:

    Summer-borns tend to lose out at school because, in England and Wales, 1 September is the cut-off date for school entry, so they can be up to a year younger than their classmates.

    June baby Frank Lampard

    Research by the Institute for Fiscal Studies two years ago found only 53% of girls and 47% of boys born in August reached the expected educational level at age seven in state primary schools in England, compared with 80% and 70% of those born in September.

    Their sporting prowess is affected too. Older children tend to be bigger and more confident, receive more encouragement, and their advantage grows over time. For unto everyone who hath shall be given.

    Among the 25 most capped England football players, 11 were born between September and November, while only one, Frank Lampard, was born between June and August. In his case, having an England international for a father probably outweighed the disadvantage.
    So for educational and sporting opportunities, the cruellest and kindest months sit next to each other in the calendar like resentful neighbours.